In conventional audio systems, a channel-based approach is employed. Each channel may for example represent the content of one speaker or one speaker array. Possible coding schemes for such systems include discrete multi-channel coding or parametric coding such as MPEG Surround.
More recently, a new approach has been developed. This approach is object-based. In systems employing the object-based approach, a three-dimensional audio scene is represented by audio objects with their associated positional metadata. These audio objects move around in the three-dimensional scene during playback of the audio signal. The system may further include so called bed channels, which may be described as stationary audio objects which are directly mapped to the speaker positions of for example a conventional audio system as described above. At a decoder side of such a system, the objects/bed channels may be reconstructed using downmix signals and an upmix or reconstruction matrix, wherein the objects/bed channels are reconstructed by forming linear combination of the downmix signals based on the value of the corresponding elements in the reconstruction matrix.
A problem that may arise in an object-based audio system, in particular at low target bit rates, is that the correlation between the decoded objects/bed channels can be larger than it was for the encoded original objects/bed channels. A common approach to solve such problems, and to improve the reconstruction of the audio objects, for example as in MPEG SAOC, is to introduce decorrelators in the decoder. In MPEG SAOC, the introduced decorrelation aims at reinstating a correct correlation between the audio objects given a specified rendering of the audio objects, i.e. depending on what type of playback unit that is connected to the audio system.
However, known methods for object-based audio systems are sensitive to the number of downmix signals and the number of objects/bed channels and may further be a complex operation which depends on the rendering of the audio objects. There is therefore a need for simple and flexible methods for controlling the amount of decorrelation introduced in the decoder in such systems, thereby allowing for improved reconstruction of audio objects.
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